Multitank aircraft fuel system



D. SAMIRAN MULTITANK AIRCRAFT FUEL SYSTEM Jan. l, 1952 2 SHEETS-SHEET l Original Filed May 15, 1945 Jan. l, 1952 D. sAM'IRAN 2,580,467

MUI T ITANK AIRCRAFT FUEL SYSTEM Original Filed May 15, 1945 2 SHEETS- SHEET 2 Patented Jan. 1, 1952 MULTITANK AIRCRAFT FUEL SYSTEM David Samiran, Fort Wayne, Ind.

Original application May 15, 1945, Serial No. 593,917, now Patent No. 2,516,149, dated July 25 1950. Divided and this application December 23, 1949, Serial No. 134,793 l 3 Claims. (Cl. 15S-36.5)

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) The invention described herein may be manufactured and used by or for the United States Government for governmental purposes without payment to me of any royalty thereon.

This invention is a division of my copehding application Serial No. 593,917, filed May l5, 1945, now Patent No. 2,516,149 issued July 25, 1950 and relates to aircraft fuel systems.

This invention relates to fuel systems for aircraft, having particular reference to aircraft for long range missions.

In modern aircraft, particularly in warcraft, it has usually been the practice to carry the fuel supply in a series of separate tanks distributed as uniformly as practicable throughout the craft, this practice having the advantage of better weight distribution and. the further advantage that if one tank becomes so punctured as to lose its fuel, the loss will be proportionately less as the number of tanks is greater.

In the more recently proposed fuel systems of this kind, automatic means are usually provided which includes means sensitive to a pressure drop at the carburetor due to an empty tank condition for disconnecting the empty tank from the suction side of the main fuel pump, searching out a full tank, and connecting the pump suction side thereto. Since, with this arrangement, there is an elapse period between the time at which a tank becomes empty and the time at which this fact registers on the pressure sensitive device at the carburetor intake, it is required, in order to insure against engine failure, to provide an emergency pump to pump fuel directly to the carburetor, s uch emergency pump being operative automatically the instant the device at the carburetor senses the drop in pressure at that point. The emergency pump then continues to operate until the engine pump has built up the pressure at the carburetor by virtue of its reconnection to a full tank. l

The practice of employing an emergency pump and connecting it to the discharge side of the engine pump to maintain the fuel pressure at the carburetor between the time that a tank becomes empty and the time that a full tank has been selected and connection made thereto, is not broadly new in this application, since such a system is shown, described and claimed in my copending application Serial No. 475,683, led February 12, 1943, now Patent No. 2,406,854, issued September 3, 1946. Moreover, fuel systems emplaying, in addition to the engine pump, an electric booster pump to discharge into the suction side of the engine pump when the fuel cavitates` 2 at this point, due to reduced atmospheric pressure at high altitude or to other causes, are also well known in the art.

In the copending application of Samiran and Mills, Serial No. 494,128 filed July 9, 1943, now Patent No. 2,435,982, issued February 17, 1948, we disclose a fuel system in which the engine pump is supplemented both by an electrically driven emergency pump and an electrically driven booster pump of the character above described. Insofar Yas known to applicant, however, a single electrically driven pump has not heretofore been made to perform both functions.

In long distance missions, particularly in long range bombing missions, where maneuverability is not a requirement during flight to the objective but is highly important after arrival at the objective, it is current practice to provide a series of externallyborne drop tanks, the fuel in which is preferably used first in getting to the objective and the crop tanks then discarded.

It is therefore an object of this invention to provide a series of drop tanks so mounted on the cralt and so connected to the system and to each other that their fuel will be withdrawn uniiormiy, part out of each tank so as to maintain a balanced condition until the fuel in the drop tanks is exhausted.

Another object of the invention is to so construct, arrange, and connect the drop tanks that, with a single setting of the selector cock, which connects the main pump to the main tank, the entire contents of the urop tanks will be transferred to the main tank as fuel is being used out oi' the main tank.

Other oblects and advantages will become evident as the invention is described in detail and reference is maoe to the drawing, wherein:

`Fig. l is a schematic view of the complete system with its hydraulic and electrical connections.

Fig. 2 is an axial section through the jaw clutch through which power is appiied to drive the automatic selector cock.

Figs. 3 Vand 4 are axial sections showing the closed and open positions, respectively, of apressure sensitive switch which shows when a tank from which fuel is being taken is empty.

Figs. 5 and 6 are transverse sections showing the closed and open positions, respectively, of a manually openable switch for deenergizing a solenoid which, when energized, maintains power connection to the tank selector cock.

Figs.` '7 and 8 show open and closed positions, respectively, of the piston valve which `prevents operation of some of the functions of the system except when the engine is running.

Referring now to the drawing, an aircraftV for illustrative purposes, may in the instant case be taken as fifteen pounds. also be provided with a small adjustable leakage passage from the discharge side back to the intake. Such a leakage passage will return only a minute volume of fuel from the discharge side back to the intake side, but when thepump is pumping air only, will return a Volume of air equal te lsubstantially the entire air pumping capacity of ,the pump from the` discharge side back to the intake side. The provision of the leakage opening thereforedoes not materially affect the capacity of the pump to raise the fuel pressure to the desired value, but` insures that when the pump is pumping air noV considerable air pressure may build up at the -carburetor intake. eliminating feature of the engine pump is shown, described and claimed in my copending application Serial No. 570,938, led January 1, 1945, now Patent No. 2,431,345, issued November 25, 1947.

A main tank I6 andan auxiliary tank I8 are carried within the aircraft` as a permanent part thereof. The main tank I6 is so arranged that the reserve portion I1 of its contents which extends from the bottom to the line I9 may not be drawn Vfrom thetank except for emergency use until after the other portion 2| above the line I9 and all fuel in the'other tanks has been used. A belly tank 2E) and wing tanks22 and 24 are carriedexternally on the underside of the fuselage and under theleft and right wings respectively. The external tanks 20, 22 Vand 2,4 may conveniently be referred to as the drop tanks.

A fuelV cock 26 has seven equally spaced stations to which the pointer 28 may be turned, namely Off, B, L, Ri, A, M, and Re when proceeding anticlockwise. These indicia, with the exception of Offv show the stations of inflow into the selector cock.

A single outflow pipe 30 emerges from the center of the selector cock, flowing first through a strainer32, then through a pipe 33 to the suction side of the engine pump I2. A pipe 34 connects the bottom of the belly tank 2l] to the inflow station B, a branch 35 extendingl upward into the top of the tank I6. A manual valve 37| in the branch 35 is normally closed. A pipe 3B connects the bottom of the left wing drop tank 22 to the inflow station L. A pipe 38 connects the bottom of the right Wingv drop tank 24 to the inflow-station Ri. A pipe 40 connects vthe bottomA of the auxiliary tank Ithrough an auxiliary pump 42, which ris driven by an electric motor 44, `to the inlowstation A. An adjustable resistance 43 is employed to regulate. theY output pressure of the pump. A manual switch 45 is provided to disconnect the pump motor 44 from its current-source.V A pipe 45 connects the bottom of the main tank I6 through a pump4 50 and branch pipe 48, to the discharge sideoI' the engine pump I2 through a pipe 53 and check valve 52, and .to the inflow passages vM and Re through the p ipe The air It may preferably...

a. A rotatable member of the selector cock 26 is secured to the pointer 28 for rotation therewith and this member is provided with a channel 55 for selectively or sequentially connecting the several inflowV passages tothe outow pipe 3Q. The pump 5i? is driven by an electric motor 54, and is so arranged and connected in the system that it may act as a booster pump, drawing from the. main body of vfuel 2| in tank I6 and delivering it to the suction side of the engine pump as an aid thereto, or it may operate as an emergency pump, drawing fuel from the reserve I1 and delivering it to the discharge side of the engine-pump when, for any reason, the engine pumpfails to maintain a predetermined pressure at the carburetor intake. Pump is provided With an inbuilt relief valve which is set to. maintain the pressure at its discharge side somewhat below that of the engine pump. For illustrative purposes the discharge pressure of pump` 5Il.may betaken at twelve pounds.,

a means for sensing when the engine-pump has failed to maintain the predetermined pres.- sure at the carburetor intake, there is provided a fuel pressure sensitive electric switch 5.6 which is connected by a pipe 58 to the discharge side` of the engine pump I2 and to the intake -of the carburetor I4. SwitchS-comprizses a body in two parts, 5G and 6I, the interior being dividedinto two compartments, 65 and 61,I the lower come partments 65 being vented to the atmospherey at 53. A spring-metal diaphragm 62 separates the compartments vandv 61, the diaphragm being slightly dished so that. it will resist change` in position from that shown in Fig. 3 to that shown in Fig. 4, er vice versa, with a resistance of apprximately two pounds. The spring 645s so proportioned that, in Fig. 3, it exerts` an upward pressure of 1l yand 1%; poundsand in Fig. 4, an upward pressure of 1 4and'1/3 pounds.` It follows that when the switchA is closed as in Fig. 1, with the switch. contacts GandV 678 in engagement, there is a resistance to downward movement of l1 and 1%, plus 2:13 and pounds, Switch 56 will accordingly open if a pressure Qf 13 and l/g pounds is appliedin the chamber 5L Conversely, whenthe switch is open as Fig.-v

4, with; theswitchcontacts. Bsand, 68 separated. there is an upward pressure of 14 and 1/8y pounds -2 pounds=12and 1,/8 pounds. A .dropI in pres: Sure. in the chamber 61 to 12 pounds wllaord: ingly allow theswth to close. It wil-1.9i course, be understood that the 'pressures atwhich the switch 56 chaneesfrom Closed t0 opennositien and vice versa, are arbitrarily chosen. for pur.

poses. of illustration and that any quiv make and break pressure. operated Switch baring; appropriate vQverlem between.. opening and.V clesing pressure, so las to prevent hunting,Y wil'lwbe consideredwithin, the scope of the invention. A warning signal light 1B is connected to the'contact member 58 whereby the light comes .on 4coincidentally with a drop yin pressure4 sufficientto the air pressure being maintained. Pipes 92 and 94 connect the bottoms of the drop tanks 22 and 24 to the top of the drop tank 20, whereby, by maintaining a proper air pressure at the gauge 90, the fuel may be forced out of the drop tanks 22 and 24 into the drop tank 20, and out of the drop tank 20 into the pipe 34 from which it may be directed by way of station B of the selector cock 26 directly to the suction side of the engine pump I2, or. by opening the valve 3|, through the main tank I6, pump 50, pipes 48 and 53 to the discharge side of the engine pump I2.

Weighted floats 96 and 98 operate conical valves and |02 in tanks 22 and 24, whereby these tanks empty uniformly and maintain a balanced load on the wings, for. if one tank empties faster than the other. the greater height of the float in the fuller tank increases its outflow passageway through the conical valve of the fuller tank and thereby maintains the balance. When the tanks 22 and 24 have been emptied by air pressure as above described, the valves |00v and |02 should be closed except that there should either be a slight valve leakage in the closed position, or there should be separate leakage openings |0| and |03 so that air pressure coming into the tanks 22 and 24 after they are empty may get through into the tank to pressurize the tank 20 when it is desirable to discharge its fuel in that manner.

A float |04 in the top of the main tank I6 operates a valve |06 to closed position to prevent fuel from the drop tanks entering the main tank I6 by way of the pipe 34 faster than it is being drawn irom the bottom by the pump 50.

A float |08 operates an electric switch I|0. Whenthe level of the fuel in the main tank |6 falls below the line I9. the switch ||0 closes, and thereafter the pump 50 cannot any longer act as a booster pump to deliver fuel from the main tank I6 by way of pipes 48 and 46, through station M of thev selector cock, and by way of pipes and 33 to the suction side of the engine pump |2, but can act as an emergency pump only to deliver the reserve fuel |1 by way of pipes 48 and 53 to the discharge side of the engine pump I2, and that only when the pressure in the pressure sensitive switch 56 drops below the predetermined value due to a tank from which the engine pump is taking fuel becoming empty. This is due to the fact that the electrical connection made by the switch ||0 acts in conjunction withanother switch hereinafter described to prevent the motor driven selector cock 26 remaining on either of the positions M`, Re, or Off.

The selector cock pointer 28 and the member which carries the channel 55 which selectively or sequentially connects the inflow positions B, L, Ri, A, M and Re to the outflow pipe 30, are both secured to the cam shaft |2 to rotate therewith. Also fast on the cam shaft ||2 is a cam ||4 which has as many notches I I6 in its periphery as the selector cock 26 has stations, which in the instant embodiment is seven. A switch IIB is always open as shown whenever the free end of the operating arm |20 has dropped into one of the notches 6.

Four cams |22, |24, |26 and |28, also fast on the cam shaft I|2, are provided for closing the switches A, M, Re and C respectively, the operating lugs on the cams |22, |24 and |26 being so positioned that the switches A, M and Re close only when selector cock pointer is set on A, M or Re respectively, while the lug on the cam |28 is so made as to keep the switch marked C closed when the selector cock pointer is on either M or Re or Oif. and open on all other stations.

A disc |32a (see Figs. 1 and 2) is fast on the rear end of the cam shaft ||2. Disc I 32a and a second disc |32 are joinedtogether at the edges by a yoke |44. A tubular part |34 extends rearwardly from the disc |32 and carries a toothed clutch part |31 at the free end. A switch |36 is operable by a plunger |3| (see Figs. 5 and 6) which lies between the discs I32a and |32.

6) into which the V end of the plunger |3I isheld by the spring |42 when the switch is closed as in Fig. 5. Rotation of the cam |30 by the shaft |35 in either direction will raise the plunger |3| and open the switch |36 as seen in Fig. 6. The yoke |44 terminates in a stop |45 (see Fig. 5) which prevents the plunger |3| ever rising high enough to get wholly out of the notch |43. It will be understood that the discs |32a and |32 with their connecting yoke |44 always rotate with the shafts ||2 and |35.

A gear |46 has a prolonged tubular hub I 48 with a flange |50. An electric motor |5I has an inbuilt high reduction gear box |53 through which a pinion |55 is driven, the pinion being in constant mesh with the gear |46. A spring |52 reacts against a stationary part |54 of the structure to move the flange I 50 into engagement with the stop |56. A solenoid coil |58 receives electric current through the switch |36 and, when energized, moves the hub |48 in the direction of the arrow |60, whereby the toothed clutch |62, which has one toothed part |31 on the tubular end |34 and the other toothed part |39 on the gear |46, will be engaged, and the switch I as well as the jaw clutch |62 will be closed. Switch |65 is connected in series with the time delay switch II 8, whereby, when the engine pump I2 restores the interrupted pressure in the fuel pressure sensitive switch 56, which thereby cuts the direct line to the `motor |5|, current will nevertheless be maintained at the motor terminal through the` switches ||8 and |65 as long as the pointer 28 is intermediate two stations. A selector handle |64 is fast on the outer end of the shaft |35. A grooved collar |66 fast on the shaft |35 is engaged by a stationary part |68 to allow rotation but prevent axial movement of the shaft. Inasmuch as the frictional resistance to rotation of the selector cock 26 must be overcome by the handle |64 when manual operation of the selector cock is being effected, it follows that, as soon as a slight torque is manually applied to the handle |64, to turn the cam I 30 the switch I 36 opens as in Fig. 6, the coil |58 is thereby deenergized, the clutch |62 is disengaged by the spring |52 and the switch |65 is coincidentally opened, whereby the motor |5| need not be manually rotated through the high reduction gearing each time the selector cock is manually operated.

Since it is desirable that certain parts of the fuel system should not become operative except when the engine is running, there is provided a switch mechanism |10 which is responsive to the oil pressure of the engine lubricating system.`

Switch rIIII comprises a contact bar |12 movable#` pump. This procedure is quite satisfactory since flying during this period is for the most part at low altitude. However, if it becomes necessary to go to a relatively higher altitude while the drop tanks have not yet been emptied, resort is had to pressurizing the drop tanks by the motor driven air pump 14 which is used also at low altitudes under certain conditions hereinafter to be described. The air pressure regulator 88 may be set to zero when it is undesirable to pressurize the drop tanks. However, when the drop tanks are emptied, and station A is reached by the selector cock pointer 28, hydraulic connection is made from the permanent auxiliary tank I8 through the booster pump 42, whereby fuel from the tank I 8 reaches the suction side of the engine pump at a considerably increased pressure.

coincidentally with the making of hydraulic connection from the auxiliary tank I8 through the booster pump 42 and station A of the selector cock 26, the cam |22 closes the switch A and provides current to the booster pump motor 44 throughout the emptying of the auxiliary tank I8. When the auxiliary tank I8 is empty the same failure of pressure at the pressure responsive switch 56 moves the selector cock pointer 28 from station A to station M, whereby the cam |22 opens the switch A and the cam `|24 closes the Switch M.

The closing of the switch M brings current from the battery |86 to the motor 54 of the pump 58 irrespective of whether the pressure responsive switch 56. the relay switch |98, or the oil pressure switch |18 are open or closed, whereby the pump 58 will act as a booster pump and draw fuel from the main tank I6 and deliver it to the suction side of the engine pump I2 until the level of the fuel drops below the line I8,

26 through the iloat switch I I8 and the fully closed oil pressure switch |18, and will rotate the selector cock anticlockwise. During movement between stations the flow of fuel past the fuel cock 26 to the suction side of the engine pump is of course interrupted, and the pressure responsive switch 56 closes momentarily between each station. When the pointer passes Re the suction side of the engine pump may momentarily get fuel from the reserve I1 and will therefore open the pressure responsive switch 56 which normally controls the selector cock motor I5I. But this time the opening of the switch 56 will not stop the motor I5| for it is now receiving current independently of the switch 56 through the reserve oat switch I|8.

Now inasmuch as, in the operation of the system above described, all other tanks were emptied before connection was made to the reserve supply |1, the selector cock will continue to rotate round and round until the operator observes that the warning light continues to be lit. He then manually operates the handles |88 and |82 of the oil pressure switch |18 so as to withdraw the contact members |16 and |18, whereupon no electrical connection will exist to the selector motor |5|. The operator may now manually place the selector pointer 28 on station Re whereupon current will ow from the battery through the cam operated switch Re to energize the coil |92 and close the switch |98 whereupon current will ow to theV motor 54 of pump 58 and fuel will be pumped from the reserve I1 to the suction side of the engine pump I2.

In the foregoing description of the operation of subject fuel system it was assumed that at the start the pointer 28 was at the Off station and that the entire system was permitted to function automatically thereby emptying the tanks in their normal anticlockwise sequence. It may happen, however, that the pointer may have been inadvertently or intentionally placed at a different station, as for example on station A.

rlhe carburetor may now be primed, vif necessary, by means of the pump 58 as hereinbefore described. When the engine is started, the fuel pressure sensitive switch 56 will still be closed whereby the selector cock motor will attempt to rotate the selector cock away from the A station, but before it can move it as much as the several degrees necessary to close the delayingI switch I I8, the engine pump will have raised the pressure at the carburetor enough to open the pressure sensitive switch 56, after which fuel will be taken from the auxiliary tank I8 through the station A until this tank is empty.

The closing of the pressure sensitive switch 56 due to this empty tank condition will start the selector motor I5I which will move the pointer 28 to station M, whereby it may take fuel from main tank I6 down to the line I9 Vwhereupon'the float switch I I8 is closed and will therefore operate in conjunction with the fully closed oil pressure operated switch |18 to maintain connection to the selectormotor I5I independently of the pressure sensitive switch 56.

The selector cock will therefore rotate anticlockwise round andround until the pilot observes the continued operation of the signal 18 whereupon he may operate the handle |88 of the oil pressure switch |18 thereby withdrawing the contact |16 from the contact |12, and the pointer will stop, except that because of the cam switch C, it cannot stop on station M, Re or 01T, and because of the time delay switch I|8 it cannot stop between stations.

If the pilot now stops rotation of the selector with the pointer at station B. he may use all of the fuel in the three drop tanks without further change of stations after which the warning light 18 will indicate to him that-he shouldnow shift to station Re and use the reserve supply I1.

If the pilot desires, he may operate the system by opening the oil pressure switch |18 so as to eliminate the selector motor |5| altogether, then open the valve 3| and set the pointer at. station A and use the fuel from auxiliary tank I8 rst, then when the warning light 18 indicates an empty tank, shift the selector cock manually to station M. The booster pump 58 will act as an emergency pump to pump to the discharge side of the engine pump and thereby maintain pressure at the carburetor until the shift has been made, whereupon the signal light 18 will go out and the pressure sensitive switch 56 will open.

Opening of the pressure sensitive switch 56, however, does not stop the motor 54 of the pump 58 for the reason that the motor 54 now receives current by way of the cam operated switch M. The pump 58 therefore now takes fue1 from the main tank I6, `pumps it through the pipe 46 through the selector cock 26, pipes 38 and 33 to the suction side of the engine pump I2 which in turn raises the pressure still further at the carburetor. Since the drop tanks are pressurized and the hand valve 3| is open, the entire remaining supply of fuel will pass from the drop tanks through the main tank and from the main tank to the suction side of the engine pump, the float vl1 valve 106 inxthez meantime;=preventing. inflow into 'the' .tank I 6:: faster than it ,is VUbeing Vusecl ^there from.

1 Still ianother'procedure ln-fcperating the system may be carried outzasfol-lows:

By placing the selector cock on station A, opening'the: hand'valveiSl landthe oil pressure responsive lswitch H0, the Aiuel in theauxiliary tank .18 will rst be pumped tothe suctionl'side of the engine pump, the engine pump raising it to Vazslightly higher pressure at the carburetor. When tank I8 isk empty, Athe pressure sensitive switch 56 `will close, whichwill coincidentally close vthe switch. |99 whereby current will be directedto thezmotor 54 of the `purnp 50.

Now the pump- 50- cannot pump through pipe because the selector cock is-on station A,:so it pumpstothezdischarge side of the engine pump .throughpipe .53. Since the 'drop .tanksare pressurized.- andA the hand .valve `3,! isy'open, the .entire ifuel :supply-p is usedxwithxthe: single setting. on station A. It issnoted that r,with this method'of operation the engine pump isusedonly 4while .the auxiliary. tank, I Bis -beingpumped out.

Having described my invention and several Ways in .which it may'beoperatedl claim:

k1. Anairoraftffuel system which comprises a main fuel tank, right and leftwing tanksand a bellyV tank, vfuel transfer :conduits connecting the bottoms of the wing tanks to the top of the Ybelly tank, aiuel ,transferzconduit forconnecting the bottom' of the bellyatanktoithe main tank, a fuel withdrawing conduit vfor withdrawing fluid4 from the. ,bottom-ofthe mainatank, Vair pump Aandeonduit means foraloplyingairy pressure to; the tops of the' wingvtankszfor transferring-fuel'frorn the bottoms.: of `.the wingtankszto the top. ofthe vbelly tank,` said fair. 4pump 'and conduit means, when said wing tanksare empty,;being also adapted yto apply air pressure .throughasaid 'wing tanks to the .top of"the.. b elly stank, thereby. forcing fuel from the Abottom f of the ebelly tank into the main tank, and a float valve in each wing tank each adapted ,to close more as :the .fuel level in said wing tank :becomes less, vwhereby-'the pressure maynot empty one. of said wingztanks .faster than the other.

` 2. Anaircraftzrfuel #system which "comprises right'and left wing.r tanks and .a .belly tank, wingvto-belly conduits extending from the .top of .the

.belly tank through the tops of the wing tanks to-points near the bottom of vsaid wing tanks, means for applying air pressure lto .the 'tops of the wing tanks, and a .belly-tofmain Yconduit eX- tending from the :bottom of the-'belly tank `for connection to thev main tank, a .float valve'in .each wing tank each adapted to close more-.as the-fuel level infsaid Wing tank becomesless, and a leakage ,opening in one .portion of the wing-to- .belly :conduits Withinzthe vwing tanksxthrough fwhich Asaid pressure -mayact `,tl'ntouglfi theV `wing tanks to the bellytank when saidA wingftanks lare empty` andisaid float valves are closed. 3. .In anzaircraftfuel system, a paiinol'` wing tanks .disposed in-.laterally .spaced relation with respectto theplane of'symmetry ofthe aircraft, discharge .conduits yassociated with saidtanks for Vdiscl'iargeinto ,a-eommonline, a 'source of.ar under pressure 'connected vin common 'to the ltop vof each l.tank .toapply airpressure' to fthe' :fuel therein, and 1a float actuated discharge throttling valve inieach tank `adapted .to reduce .the discharge vas the fuel level in each tankbecomes less thereby to. maintain substantial .synchronism withrespeot'to fuel level "in the tanksv `during discharge.

DAVID ,SAMIRAN REFERENCES CITED VThe' following `references are Yof record in the lile of this patent:

.UNITED STATES PATENTS Number vName -A.Date

.1,367,460 Caudron Feb. v1', 41921 1,407,374 :Buckendale Feb.:2l, 1922 1,776,877 Yonkcse Sept. 30,1930 2,394,506 fWoods fFeb. 5,1946 2,409,245 Black --Oct..15,;l946

` FOREIGN PATENTS Number Country v-Date .111,006 GreatBritain Nov..15, 191'7 .146,446 Great .Brta11. V July .3, 1920 Y:653.053 .France Oct.,30., 1928 

